1. Field of the Invention
The present invention relates to three-way valves useful for semiconductor production equipment, food processing machines, etc. which must be very clean.
2 Description of the Prior Art
It is frequent to clean the piping of semiconductor production equipment, biotechnological and food processing machines, etc. with an inert gas, such as a nitrogen gas, water, or steam, in order to assure the clean piping.
FIG. 8 shows a conventional piping in which two two-way valves 15a and 16a are installed in the downstream portions of a pipe 15 for semiconductor production equipment, for example, and a pipe 16 for carrying a cleaning fluid to the pipe 15. A primary fluid and a cleaning fluid enter at inlets 15A and 16A, respectively, and exit from an outlet 17A as indicated by solid arrows.
However, in the above arrangement there is a residence space S between the two-way valve 15a and a connection fitting 17, making it difficult to clean the area. The same is true in cleaning the upstream portions of the pipes as indicated by broken arrows. Thus, it is necessary to install the two-way valves 15a and 16a as close as possible.
In FIGS. 9 and 10, in order to minimize the residence space, it has been proposed that two two-way valves 18A and 18B are integrated to eliminate the connection fitting. A primary fluid and a cleaning fluid enter at inlets 19 and 20 and exit from an outlet 21.
However, there is still a residence space although it is reduced. The cleaning time of this arrangement is much shorter than that of FIG. 8, but there is room to be improved.
In order to solve such problems, the use of three-way valves has been proposed such as a ball valve of FIG. 11 and a slide valve of FIG. 12. There seem no residence spaces in these valves. However, it is necessary to provide some gaps between sliding parts 22 and 23 and opposed walls 24 and 25, resulting in the creation of residence spaces. The volume of these spaces is much smaller than that of the case where two-way valves are used but, upon cleaning, there can be backflows of a fluid remaining in the gap, thus presenting a serious problem.